To make the crust: In a medium bowl, mix together the graham cracker crumbs, melted butter, and granulated sugar until the crumbs are evenly moistened. Press the crumbs firmly and evenly onto the bottom and up the sides of the prepared pie pan. Bake until the crust looks lightly toasted, about 15 minutes. Cool completely.

To make the filling: Sprinkle the gelatin over the water into a small bowl. Set aside.

In a heatproof medium bowl, whisk together egg yolks and half a cup of the sugar until thick and lemon colored. Whisk in the lemon zest, lemon juice, and the salt.

Place the bowl over a saucepan of briskly simmering water (the bottom of the bowl should not touch the water). Whisk constantly until the sugar is dissolved. With a rubber spatula, stir the lemon mixture, scraping down the sides of the bowl, until it thickens and read 185 Degree F on an instant-read thermometer; 5-7 minutes. It should be thick enough that your finger will cut a swath when you run it over the mixture on the spatula. Remove from the heat, add the gelatin mixture, and stir well to completely dissolve the gelatin.

Strain the lemon mixture through a wire sieve into another medium bowl set in a larger bowl of iced water. Let stand stirring often, until the mixture is chilled and beginning to set, about 10 minutes.